1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a message transmission method and apparatus for location estimation in a wireless communication system.
2. Related Art
User equipment (UE) positioning for estimating a location of a UE has recently been used for various usages in real life, which requires a more accurate UE positioning method. The UE positioning method can be roughly classified into four methods as follows.
1) Global positioning system (GPS)-based method: In this method, a satellite is used to estimate the location of the UE. Information must be received from at least four satellites. Disadvantageously, this method cannot be used in an indoor environment.
2) Terrestrial positioning-based method: In this method, the location of the UE is estimated by using a timing difference of signals transmitted from base stations (BSs). Signals must be received from at least three BSs. Although this method has lower location estimation performance in comparison with the GPS-based method, it can be used in most of environments. A signal received from the BS may be a synchronization signal or a reference signal (RS), and according to a wireless communication system in use, can be defined in various terms, such as observed time difference of arrival (OTDOA) in UMTS terrestrial radio access network (UTRAN), enhanced observed time difference (E-OTD) in GSM/EDGE radio access network (GERAN), advanced forward link trilateration (AFLT) in CDMA2000, etc.
The RS can be used to estimate the location of the UE. The RS may include a synchronization signal. The UE can receive RSs transmitted from multiple cells, and can use a difference in a time delay of each signal. The UE may report the difference in the time delay to the BS so that the BS can calculate the location of the UE, or may autonomously calculate the location of the UE. Referring to the section 4.1.1 of 3rd generation partnership project (3GPP) long term evolution (LTE) TS36.355 V9.0.0(2009-12), an enhanced serving mobile location center (E-SMLC) can use a LTE positioning protocol (LPP) to control measurement values such as a reference signal time difference (RSTD) measured by the UE. The LPP can be defined as a point-to-point between a location server (e.g., E-SMLC, etc.) and a target device (i.e., UE, etc.) so that a location of the target device can be estimated using a location relation measurement value obtained from one or more RSs.
Meanwhile, RS transmission for UE location estimation may be muted. That is, a cell may not transmit the RS in a specific situation. This is because, when the UE receives an RS from a reference cell or a neighbor cell, strength of an RS received from the reference cell may be significantly greater than strength of an RS received from the neighbor cell, and in this case, the RS received from the neighbor cell may not be properly decoded. The UE needs to exactly know a muting pattern of RSs transmitted from multiple cells. The UE can recognize a muting pattern of an RS of each cell on the basis of at least one cell. However, due to such a reason as a handover of the UE or an asynchronous network or the like, there is a possibility that ambiguity occurs in which the UE cannot accurately recognize a muting pattern of an RS transmitted by each cell.
Accordingly, there is a need for a message configuration and transmission method by which a UE recognizes a muting pattern of an RS.